Many handheld communication devices now have the capability of receiving and processing GPS signals. The GPS antennas of these devices are usually embedded internally, and separated from the other communication systems. Those antennas are narrowband in nature, since they only have to cover a very narrow portion (about 10 Megahertz (MHz) of the spectrum around 1575 MHz, while minimizing interaction with any other communication system antennas within the same device. Due to the narrow bandwidth of these antennas, they are particularly sensitive to changes in the proximate environment, such as loading associated with a user's hand. Small changes in the proximate environment can produce a significant detuning of the antenna and, consequently, greatly deteriorate its performance (efficiency). Many times, these changes in proximate environment are unpredictable and user dependent.
Typically, in the free space environment the GPS internal antenna is designed to have peak efficiency around 1575 MHz (the GPS transmit frequency). However, when a user holds a handset while operating in the GPS mode, the GPS internal antenna becomes detuned. As a result, the GPS performance in actual usage is much poorer than measurements in free space due to the losses that result from human hand absorption and reflection due to impedance mismatch.
Conventionally, the GPS antenna in a handheld device has no matching network, or if present, its tuning is fixed for a particular topology and proximate environment. With an increased demand for an improvement in indoor sensitivity, and support for emergency calls and LBS (Location Based Services), a need for improved GPS antenna performance is desirable. A tunable matching circuit that could correct for the detuning effect of the proximate environment upon the antenna, would enhance the performance of the antenna and of the overall GPS link for any given environment scenario.